It is well established that surgical patients under anesthesia become poikilothermic. This means that the patients lose their ability to control their body temperature and will take on or lose heat depending on the temperature of the environment. Since modern operating rooms are all air conditioned to a relatively low temperature for surgeon comfort, the majority of patients undergoing general anesthesia will lose heat and become clinically hypothermic if not warmed.
Several companies have developed electric warming blankets that can be placed over patients during surgery. However, these electric blankets have a number of inadequacies. For example, a patient may suffer thermal burn injury if the blanket is accidentally left in contact with the skin for a prolonged period of time or if a portion of the blanket becomes faulty and overheats.
To prevent blanket overheating, companies have included one or more temperature sensors in a blanket that can sense the temperature in a desired area and then provide feedback to a control system. The temperature sensor can be placed in an area that would be in contact with a patient or in an area that would reflect an average temperature of the blanket. The control system shuts off the power supply and/or triggers an alarm if the sensed temperature is too high. Thus, the temperature sensor acts as a safety feature to help protect patients from blanket overheating.
However, while a temperature sensor can help prevent blanket overheating, additional safety features would be desirable in case the temperature sensor does not reliably report an accurate average temperature of the blanket. This can happen in a number of situations. In some cases, the temperature sensor itself may simply be damaged and may provide false information to the control system. In other cases, the temperature sensed may be cooler than the temperatures of other areas of the blanket. This could occur, for example, if a cool object such as a metal pan or an ice bag is placed on the blanket near the temperature sensor. The cool object acts as a heat sink and absorbs heat from the blanket, causing the area near the sensor to feel cooler. In another example, the area of the blanket near the temperature sensor may become wet or damaged. In each of these examples, the temperature of the blanket in the temperature sensor area is cooler than the temperature of other areas of the blanket. The cool sensed temperature allows the control system to continue supplying power to the blanket, even though the temperatures in the other areas are too high. The other temperatures would continue rising to excessive levels and body parts in contact with these areas of the blanket may suffer thermal burn injury if in contact with the blanket for a prolonged period of time.
Accordingly, there is a need for a blanket that incorporates an additional safety feature other than a temperature sensor. Further, there is a need for a blanket that incorporates a safety feature that prevents a patient from being exposed to excessive heat for a prolonged period of time. Various embodiments of the invention described herein solve one or more of the problems discussed above.